As transistor design is improved and evolved, the number of different types of transistors continues to increase. Multi-gate fin field effect transistors (e.g., FinFETs) are developed to provide scaled devices with faster drive currents and reduced short channel effects over planar FETs. One feature of the FinFET is that the conducting channel is wrapped around a thin silicon “fin,” which forms the body of the device. The dimensions of the fin can determine the effective channel length of the device. The term “FinFET” is used generically to describe any fin-based, multi-gate transistor architecture regardless of number of gates. Examples of multi-gate fin field effect transistors include double-gate FinFETs and tri-gate FinFETs.
Double-gate FinFETs are FETs in which a channel region is formed in a thin semiconductor fin. The source and drain regions are formed in the opposing ends of the fin on either side of the channel region. Gates are formed on each side of the thin semiconductor fin, and in some cases, on the top or bottom of the fin as well, in an area corresponding to the channel region. FinFETs are generally a type of double-gate fin FETs in which the fin is so thin as to be fully depleted.
Tri-gate FinFETs have a similar structure to that of double-gate FinFETs. The fin width and height of the tri-gate FinFETs, however, are approximately the same so that gates can be formed on three sides of the channel, including the top surface and the opposing sidewalls. The height to width ratio is generally in the range of 3:2 to 2:3 so that the channel will remain fully depleted and the three-dimensional field effects of a tri-gate FinFET will give greater drive current and improved short-channel characteristics over a planar transistor.